1. Field of the Invention
The present invention relates generally to a magnetic sensor and, more particularly, to a magnetic sensor that has a magnet and magnetically sensitive component encapsulated within a solidified quantity of thermoset material without the need for a carrier to hold the magnet and the magnetically sensitive component in place relative to each other.
2. Description of the Prior Art
Many different types of magnetic sensors are known to those skilled in the art. One type of magnetic sensor incorporates a magnetically sensitive component, such as a Hall effect element or a magnetoresistive element, in combination with a permanent magnet that provides a biasing magnetic field. The magnetically sensitive component and the permanent magnet are arranged relative to each other so that the magnetically sensitive component is disposed within the magnetic field of the permanent magnet. The sensor detects the movement of a ferromagnetic object, such as a geartooth, by sensing the change in the magnetic field caused by the movement of the ferromagnetic target within the sensor's detection zone. In known sensors, a carrier of some type is used to contain the magnet and hold the magnet in place relative to the position of the magnetically sensitive component. In certain types of magnetic sensors, it is extremely important to hold the magnetically sensitive component at a precise location relative to the permanent magnet following a calibration procedure.
U.S. Pat. No. 5,121,289, which issued to Gagliardi on Jun. 9, 1992, discloses an encapsulatable sensor assembly which includes an external housing with internal support components for retaining an active sensor element and associated electrical circuitry in a predetermined relationship while providing a plurality of internal sequentially interconnected cavities for facilitating a flow of an encapsulating material from an encapsulating material injection port to a vented overflow to assure a complete fill of the internal cavities to restrain the internal components. The sensor assembly provides a structure for a void free encapsulation and internal lead wire stress relief concurrently with location control of the internal components while also providing a combination which is easily adaptable to automatic assembly and encapsulation techniques.
U.S. Pat. No. 5,414,355, which issued to Davidson et al on May 9, 1995, discloses a magnet carrier disposed within an outer housing. The carrier is shaped to retain a permanent magnet in a particular position relative to a plurality of electrical conductors and a substrate on which a magnetically sensitive component is attached. The carrier and its associated components are inserted into a housing which can be deformed to permanently retain the carrier within a cavity of the housing. All of the components of the sensor are designed to be easily assembled along a common axis to facilitate automatic assembly and manufacture of the sensor. The magnetically sensitive component can be a Hall effect element that is associated with other electrical components which are also attached to a substrate that is disposed proximate a front end of the carrier.
U.S. Pat. No. 5,444,370, which issued to Wu on Aug. 22, 1995, describes a magnetic angular position sensor with two magnetically sensitive components arranged proximate two target tracks having complementary magnetic and nonmagnetic segments. The sensor is provided with two target tracks that are arranged in generally parallel association with each other. Each of the target tracks comprises magnetic and nonmagnetic segments which are arranged in alternating patterns. Each magnetic segment of the first target track is disposed along side a nonmagnetic segment of the second track and each magnetic segment of the second target track is disposed along side a nonmagnetic segment of the first target track. First and second magnetically sensitive components are disposed proximate the first and second target tracks, respectively, and a source of a magnetic field is disposed proximate the first and second magnetically sensitive components. Distortions of the magnetic field imposed perpendicularly on the first and second magnetically sensitive components are used to provide first and second output signals therefrom. A third output signal, which is a function of the first and second output signals, is used to determine the location of the first and second target tracks with respect to the first and second magnetically sensitive components. The magnetic and nonmagnetic segments of the first and second target tracks can be different sizes and arranged in a pattern which permits the specific and absolute location of a movable object to be determined.
Sensors which comprise a hollow housing into which components are inserted and eventually encapsulated within solidified epoxy present a potentially serious manufacturing problem. The curing of the liquid epoxy requires a significant time period and often requires the use of heat to cure the encapsulating material. During the curing process, the sensor must be held in an appropriate position for an extended period of time.
Certain sensors have been developed which are encapsulated by an overmolding process, but significant care must be taken to avoid dislodging electronic components during the process if a thermoplastic material is used as the encapsulant. Because of the significant forces typically imposed on the encapsulated component during the overmolding process, the components must be rigidly attached to a printed circuit board or other type of rigid substrate prior to the overmolding procedure. For these and other reasons, known magnetic sensors provide a carrier which is typically made of plastic and shaped to receive the permanent magnet within it. The carrier is then typically used to position the magnetic relative to a magnetically sensitive component and hold the magnetically sensitive component in position relative to the permanent magnet during subsequent assembly and manufacturing processes.
The use of a plastic carrier for the purposes described above adds to the costs of the magnetic sensor and also increases its required size. It would therefore be significantly beneficial if a magnetic sensor could be made without the need for a plastic carrier to hold the permanent magnet. It would also be beneficial if a magnetic sensor could be manufactured by directly overmolding a permanent magnet and a magnetically sensitive component together with a thermoset encapsulant. It would also be beneficial if the electronic components of the magnetic sensor could be held in their respective positions on a flexible substrate to facilitate the accurate positioning of the magnetically sensitive component at one end of the permanent magnet while disposing the other electronic components along the side of the permanent magnet. When the magnetically sensitive component comprises a magnetoresistive element which therefore most must be positioned accurately relative to the permanent magnet, it would also be significantly beneficial if a means is provided to rigidly attach the permanent magnet to the magnetically sensitive component prior to the encapsulation of the sensor so that the accurate position of these components can be maintained prior to and during the encapsulating process with a thermoset material.